The present invention generally relates to a method and an apparatus for controlled linking/patterning of self-assembled, preferably nano-sized objects, and more particularly to ultra-high density data storage.
This invention can be applied to various technologies, which realization relies on a method and an apparatus for controlled linking/patterning of self-assembled objects. As a particular example, patterning self-assembled magnetic objects into object-containing dot arrays with precise control of dot size and inter-dot spacing has technologically great potential in future ultrahigh density magnetic data storage. Specifically, ultrahigh density magnetic storage requires continued down scaling of each individual storage bit. In the past, this growth of storage densities has been accomplished simply by scaling down the grain size in the magnetic media, while maintaining the numbers of grains constant within one bit cell due to signal to noise requirements in the magnetic readout (transition noise). However, this scaling approach will come to an end in the near future, because with decreasing grain size the thermal energy can reverse more easily the magnetization direction (superparamagnetism), which eventually will result in the loss of the stored information. As one approach to circumvent the superparamagnetic limit and to increase further storage densities, patterned magnetic media has been proposed. More specifically, patterned media is a solution to the signal to noise constraints by creating a xe2x80x9cdotxe2x80x9d array of magnetic entities, where each dot contains one or more magnetic grains or objects. Previous efforts in fabricating such dot arrays relied on complicated and expensive lithographic processes, including e-beam lithography [R. M. H. New, R. F. W. Pease, R. L. White, J. Vac. Sci. Technol. B, 13, 1089 (1995); C. Haginoya, et al, J. App. Phys., 85, 8327 (1999); A. Y. Toporov, R. M. Langford, A. K. Petford-Long, App. Phys. Lett., 77, 3063 (2000)], Ion beam lithography [T. Devolder, et al, Appl. Phys. Lett., 74, 3383 (1999); W. M. Kaminsky, et al, Appl. Phys. Lett., 78, 1589 (2001)], optical lithography [M. Farhoud, et al, IEEE Trans. Magn., 34, 1087 (1998)] and nanoimprint lithography [S. Y. Chou, P. R. Krauss, P. J. Renstrom, Science, 272, 85 (1996); S. Y. Chou, P. R. Krauss, L. Kong, J. App. Phys., 79, 6101 (1996). A. Lebib, S. P. Li, M. Natali, Y. Chen, J. App. Phys., 89, 3892 (2001)]. Recently, direct patterning of passivated gold nanoclusters via e-beam has been proposed and demonstrated under high vacuum conditions [X. M. Lin, R. Parthasarathy, H. M. Jaeger, Appl. Phys. Lett., 78, 1915 (2001); T. R. Bedson, R. E. Palmer, T. E. Jenkins, D. J. Hayton, J. P. Wilcoxon, Appl. Phys. Lett., 78, 1921 (2001); T. R. Bedson, R. E. Palmer, J. P. Wilcoxon, Appl. Phys. Lett., 78, 2061 (2001)]. However, good control of nanoparticle-containing dots has not been reached. In contrast to these previous efforts, the present invention offers a very simple solution by providing a potentially inexpensive method and an apparatus capable of linking and/or patterning self-assembled (magnetic) objects. While this invention has been described mostly in terms of ultrahigh density data storage, the same methods/apparatus can be applied to other important applications, of which two examples are discussed more in detail below.
As a second example, this invention may relate to fabrication of highly sensitive sensors [D. R. Baselt, et al, Proceedings of the IEEE, 85, 672 (1997); Q. Sqalli, M. P. Brenal, P. Hoffmann, F. Marquis-Weible, Appl. Phys. Lett. 76, 2134 (2000)]. Novel sensors, especially for near-field sensing, rely on a technique that can generate nanostructures preferably at the end of a sharp probe such as an atomic force microscope (U.S. Pat. No. 5,237,859) or a scanning tunneling microscope (U.S. Pat. No. 4,343,993) probe. More specifically, the present invention may allow to link a small magnetic nanoparticle (e.g. radius less than 10 nm) to the end of a, preferably heated, AFM/STM-probe, which results in high sensitivity for magnetic force sensing at high spatial resolution. Further, the present invention may be suitable to arrange a small highly polarizable nanoparticle at the end of a sharp probe (e.g., silicon probe or carbon nanotube), which can act as a small antenna greatly enhancing near-field optical sensing capabilities.
As a third example, this invention may relate to the preparation of efficient catalysts [A. S. Eppler et al., J. Phys. Chem. B, 104, 7286 (2000)]. Catalytic reactions generally require high pressure and high temperature conditions. However, current catalysts of small sized particles tend to aggregate under such conditions, resulting in the loss of their catalytic properties. This invention discloses a method and an apparatus, which avoids the aggregation of these particles, especially since the distance between the particles/islands of particles can be easily tuned.
The present invention builds upon the notion of self-assembly. Self-assembly is a low-cost and alternative (e.g., non-lithographic) way to organize objects, preferably nanoparticles, whereby these objects are used as functional building blocks for device fabrication, see U.S. Pat. No. 6,162,532, and U.S. patent application Ser. No. 09/359,638, now U.S. Pat. No. 6,254,662, both of which introduce the self-assembly of magnetic nanoparticles into magnetic nanoparticle superlattices, and are hereby incorporated by reference; and an article by S. Sun, C. B. Murray, D. Weller, L. Folks, and A. Moser, Science 287, 1989 (2000). The self-organization is influenced by the nature of the interactions exhibited among the stabilized particles. Generally, it relies on weaker and less directional interactions, such as van der Waals interactions, to organize the particles, and as a result, the assembly is not robust in its initial form. Thermal annealing has been applied to induce the transformation of organic stabilizers around each particle to polymer or inorganic matrix that can efficiently increase the robustness of the assemblies [S. Sun, C. B. Murray, D. Weller, L. Folks, A. Moser, Science, 287, 1989 (2000).].
With the invention, by applying an energy source locally to a specific area, the assembly in that area is hardened and can also adhere to the substrate well. The unirradiated self-organized nanoparticles, connected by weak interactions, can be easily washed away with a solvent as described in detail below, whereby self-assembled nanoparticle dot patterns are formed. With the invention, the height/thickness of the dots can be tuned all the way down to 2 nm via the self-assembly deposition technique, and the diameter (or lateral dimension) of the dots can be tuned down to less than 10 nm depending on the energy source used. Thermal annealing may be applied to the patterned dots to control their physical properties as well. The reported procedure does not need prior substrate modification, as in common lithographic processes, and allows for patterning on any size and shaped substrates. In summary, this invention offers a low cost solution to patterned media by providing controlled assemblies of dot arrays over larger areas, and allowing for patterning with high lateral resolution.
The present invention describes a method and an apparatus for linking and/or patterning self-assembled first object(s) (e.g., nanoparticles), to which stabilizers are attached, to (a) second object(s) (e.g., surface) by applying energy to the first object(s). The energy, which is directed, preferably locally, to the object(s) may activate a chemical reaction among the stabilizers, and cross-links the objects. As a result, the first object(s) is (are) linked to the second object. In addition, the energy may be used to alter chemical or physical properties of the particles. For example, heating of FePt nanoparticles may be utilized for linking as well as changing the phase thereby turning the particles from paramagnetic to ferromagnetic. Repeating this procedure allows the invention to arrange (and alter) objects over larger areas. In some situations, it may be desirable to remove the remaining (non-linked) objects by applying an appropriate solvent to the remaining (non-irradiated) objects. Thermal annealing may be used to control physical and chemical properties of the patterned object(s).
Accordingly, in a first aspect of the present invention, disclosed is an apparatus/assembly suitable for linking and/or patterning self-assembled object(s), preferably nanoparticles, preferably on a local scale, the apparatus comprising: self-assembled first object(s), preferably (a) nanoparticle(s); stabilizer(s) attached to the first object(s); second object(s) to which the first object(s) is linked; an energy source, which directs energy to the object(s) and/or stabilizer(s); and a controller/control mechanism for coordinating a mutual positioning of the directed energy and the object(s).
In a second aspect of the present invention, disclosed is a method suitable for linking self-assembled object(s), preferably nanoparticles, preferably on a local scale. The method comprises the following steps: providing an apparatus as described in the first aspect of the invention; self-assembling the first object(s); coordinating the mutual positioning of the incident energy and the object(s), generating and directing energy to the object(s) and/or stabilizer(s); and operating a controller so that linking is enabled by using an information signal for modulating the directed energy.
In a third aspect disclosed is a method suitable for patterning self-assembled object(s), preferably nanoparticles, preferably on a local scale. The method comprises all steps, which are described in the second aspect of this invention, as well as applying means, preferably a solvent, to remove nonlinked objects in order to generate a patterned structure, and thermal annealing.